Automatic defroster



` Feb. 1

G. BAXTER AUTOMATIC nEFRosTEx Filed Jan. 25, 1938 IN VENTOR. dear a/XlerW f ATTORNEYS Patented Feb. 1l, 1941 UNITED STATES PATET oFFlcE14Claims.

This invention relates to a mechanism for defrosting refrigerators ofthe type which are operated either by electricity or gas, although it isnot limited to such use. More specifically, the invention relates to adefrosting mechanism which is adapted to cause the rapid and effectiveremoval of the frost and ice which forms on the surfaces of refrigeratorfreezing compartments, when the ice formed thereon has reached apredetermined limiting thickness.

It is a well known fact that the water vapor present in the air whichcirculates throughout refrigerators is usually a detriment to theirproper operation since it tends to condense upon the 1| outer surface ofthe freezing compartment where it freezes and forms a solid layer ofice. Since this layer of ice is a good heat insulator, the efficiency ofthe cooling operation is greatly diminished and, as the thickness of theice in- !o creases, the cooling eifect of the refrigerator decreases, upto a point where eventually the operation becomes uneconomical. Thelayer of ice must then be removed if proper refrigeration is to beobtained.

The insulating layer of ice is ordinarily removed by shutting off thepower to the refrigerator and allowing the temperature of the aircontained therein to increase until it is high enough to m'elt the ice.'I'his operation frel quently takes as long as 24 hours, during whichperiod the refrigerator cannot be used to store perishable foods sincethe temperature therein is usually not low enough to keep them in goodcondition. Moreover, there is a tendency on the Il part of some personsto defrost the refrigerator without rst looking to see if there areperishable goods stored in it, so that these goods will be withoutrefrigeration during the delrosting period and will frequently spoil.

40 An object of the invention, accordingly is to provide a defrostingmechanism which will operate automatically to melt the ice when thedepth of the ice layer formed on the freezing compartment has reached apredetermined limmng value.

Another object of this invention is to provide a defrosting mechanism ofthe above character by means of which a refrigerator may be effecmtively defrosted within a very short period of time and withoutincreasing thetemperature of the air within the refrigerator to anyappreciable extent.

A further object of the invention is to provide u a defrosting mechanismof the above character (Cl. (S2-1) in which the ice is rapidly andeiectivelyremoved by the application of heat.

Another object of the invention is to provide a mechanism of the abovecharacter in which the thickness of the ice is periodically tested andin 5 which a circuit is closed to energize means for the removal of theice when the latter has reached a predetermined thickness.

In a preferred embodiment of the invention a mechanism for testing thethickness of the ice is provided, which comprises two members,maintained substantially at right angles to each other by suitableresilient means, and which are so mounted that one member hangsperpendicular to, and out of contact with one side of the freezingchamber of the refrigerator. Each member has a contact mounted on it,and the mechanism is so assembled that the contacts are normally open.An electromagnet is provided which is periodically energized to raise anarmature past the horizontal member of the testing mechanism. Theelectromagnet remains energized for only an instant so that its armatureimmediately falls back into position. To return to the normalinoperative position, however, it must move past the horizontal memberof the testing mechanism, causing the latter to rotate about a xedpoint. The testing mechanism is so adjusted that if a layer of ice ofpredetermined thickness has formed on the side of the freezing chamber,the armature of the electromagnet will rest on the horizontal member ofthe testing mechanism and since the vertical member is prevented frommoving by the layer of ice on the side of the freezing chamber, theweight of the armature will act to depress the spring between the twomembers to close the contacts mounted thereon. 'I'hese contacts completea circuit through a. number of series-connected heating coils which aresecured to the outer surfaces of the freezing cham- 40 ber. The heatgenerated in these coils acts to melt the ice formed on the sides of thefreezing chamber reducing its thickness until the testing mechanism hasmoved far enough to allow vthe armature of the electromagnet to dropinto the original inoperative position, when the contacts are againbroken. It is evident that with this device the thickness of the iceformed on the side of the freezing chamber may be controlled within veryclose limits, and the refrigerator may be automatically defrosted withina very short period of time without raising the temperature of the airtherein by any substantial amount.

Additional objects will be evident from the following detaileddescription of a preferred em- 56 bodiment of the invention when takenin connection with the single drawing, in which:

Figure 1 is a front view in elevation and partly in section, of anautomatic defrosting mechanism constructed in accordance with thisinvention, which is shown secured to one side of the freezing chamber ofa refrigerator;

Figure 2 is a side view, partly in section, taken through the line 2--2of Fig. 1, looking in the direction of the arrows, illustrating theconstruction of the ice thickness testing mechanism and Figure 3 is afront view, partly in section, showing the operative position of thedevice when the thickness of the ice formed on the freezing chamber hasreached the limiting value.

Referring to Figure 1, the freezing chamber of a refrigerator is shownat I0, to one side of which the three elongated bolts II are secured bymeans of the nuts I2. The defrosting mechanism comprises a housing I3 towhich are soldered or otherwise secured three elongated tubes I4 whichare adapted to receive three bolts II on the side of the freezingchamber III. At the outer extremity of each of the tubular members I4 ashort sleeve I5 is secured which is formed with an outward extension I 6which is bent downwardly to form the split lug I1. In assembling, thetubes I4 slide over the bolts I I until the housing I3 is in the desiredposition next the outer wail of the freezing chamber I0. The extremeends of the bolts I I are threaded at I8 to receive the nuts I9 in whichthe axial grooves 20 are formed to receive the split lugs I1 on theextensions I6. By adjusting the nuts I9, the housing I3 may be movedwithin a reasonable range so as to control the distance between the sideof the freezing chamber I0 and the defrosting mechanism.

At the upper end of one of the side walls of the housing I3 anelectromagnet 2I is secured by means of the through bolts 22 and thenuts 23. Directly below the electromagnet an armature 24 is pivoted at24' and is adapted to rest on a vertical stop member 25 which is securedto the base of the housing I3. The position of the armature 24 is sochosen that the air gap will be small enough to permit it to be rapidlybrought into contact with the lower surface of the electromagnet 2| whenthe latter becomes energized.

A rectangular aperture 26 is formed in the side of the housing I3 whichis nearest the freezing chamber I0, at the upper end of which a pin 21is journalled at 28 to form a hinge about which a vertically dependingmember 2l may freely swing. The upper central portion of the verticalmember 29 is bent inwardly at right angles to form an arm 30 on which aninsulated contact II is mounted. A member I2 is hinged on the centralportion of the pin 21 and is maintained parallel to the arm 30 by meansof a coil spring 33 which is mounted therebetween. On the member 32 aninsulated contact 34 is mounted which is adapted to engage the contactII on the member .iII to close a circuit for defrosting therefrigerator. The member 32 also carries a downwardly depending L-shapedguard I! which acts to prevent the contacts 3i and 34 from separatingmore than a iixed amount when the member l2 is raised by the armature24.

The refrigerator compressor motor 3i is supplied with power from asource 31 through the wires 38 and a starting box 3! which is connectedin series with the motor I0. A connection is also made from the sourcel1 through the wires 38, the starting box 39 and the wires 40 t0 io theelectromagnet 2i by means of which itv may be These last connections areso made that when the handle of the starting box l! is on the nrst pointthe electromagnet 2i is instantaneously energized. But when` the handlehas moved to the second resistance point the magnet is then deenergizedand it remains in this condition until the motor has stopped and hasstarted again.

In operation, let it be assumed that the temperature within therefrigerator has been raised to such a point that the motor starting boxI9 is operated in conjunction with the usual thermtat and electromagnet,not shown. The handieofthestartingboxbeginstomovefrom the highestresistance point to the lowest and as it passes over the iirst point itenergizes the electrolnagnet 2| through the wires 4U. The armature 24thereupon instantaneously swings upwardly until it is in contact withthe face of the et 2I and in so doing it strikes the edge of thehorizontal member 32 of the ice testingmechanism. Since the member 30andthe member I2 are connected by means of the spring Il, the entiretesting mechanism rotates in a clockwise direction about the pin 21.When the handle of the starting box ll reaches the second point theelectromagnet 2I is instantaneously deenergixed. allowing the amature 24to fall downwardly when it again engages the upper surface oi thehorizontal member 32, forcing it downwardly and causing the entiretesting mechanism to rotate in a counter-clockwise direction about thepin 21 until the armature 24 rests on the stop 2l in the normalinoperative position. 'I'he tension in the coil spring 33 is so adjustedthat the contacts 34 and SI will not be clod when the horizontal memberI2 is moved downwardly unless the vertical member 29 is held in a fixedposition. Thus, if no ice has formed on the side wall of the freezingchamber I Il, the testing mechanism will freely rotate and allow thearmature 24 to return to its normal position without closing the circuitthrough the heating coils.

When the ice formed on the side of the freezing chamber Il has reachedthe predetermined limiting thickness, the initial energizing of thecompressor motor I8 will energize the electromagnet 2l causing itsamature 24 to swing upwandly past the horizontal member 32 until theeleciromagnet 2| is again deenergized. The armature 24 then dropsdownwardly, striking the hnrlmntai member 32 which is thus also forceddownwardly, causing the testing mechanism to rotate about the pin 21. Asshown in Figure 3. however, the presence of a layer of ice of limitingdepth on 'the side of the freezing chamber Il almost immediately stopsthe movement of the vertical member 2l, so that the weight of thearmature 24 compresses the spring ss the heating progresses, thethickness of theV layer of ioe on the side wall of the freezing chamberIl is reduced, permitting the vertical member II to move outwardly lfromthe defrosting mechanism and simultaneously allowing the horizontalmember to move downwardly until eventually the amature 24 call fall pastthe member 32 to rest on the stop 2B. The relative weights oi' thehorizontal member 32 and the vertical member 29 should be so chosen thatthe testing mechanism will remain in the inoperative positionsubstantially as shown in Figure l. in which the member parallel to theside of the freezing chamber I0 is in a substantially vertical position.Furthermore, the armature 2l should be so designed that it will be heavyenough to overcome the tension in the spring 33 when -it rests on thehorizontal member 32 in the circuit closing position.

This invention provides a mechanism by means of which ice formed on theouter walls of a freezing chamber may be rapidly and effectivelyremoved. Furthermore, defrosting may be accomplished without raising thetemperature of the air within the refrigerator to any appreciable extentso that there is no possibility of perishable food being inadvertentlyspoiled, as frequently happens with other defrosting processes. Themechanism, moreover, is very simple in character and occupies a minimumamount of space within the refrigerator. This last is an importantfeature since the available space in modern electric and gasrefrigerators is very limited.

It is obvious that the automatic defrosting mechanism described abovecan be applied to a wide range of refrigerating equipment and is notnecessarily limited to refrigerators of the electric or gas type. Forexample, it might be used to determine the thickness of ice on the largefreezing coils which are customarily used in cooling large show casesand the like. It is to be understood, therefore, that this inventioncomprehends all such uses.

While a specific embodiment has been presented above, the invention isnot intended to be limited in any way thereby. but it is susceptible ofvarious changes in form and detail within the scope of the appendedclaims.

I claim:

1. An automatic defrosting mechanism comprising means to test thethickness of a layer of ice intermittently, and means responsive to apredetermined thickness of ice for applying heat to the said ice layer.

2. An automatic defrosting mechanism comprising means to test thethickness of a layer of ice intermittently, electrical means to removethe said layer of ice, and means responsive to a predetermined thicknessof the said ice layer for closing a circuit to energize the said iceremoving means.

3. An automatic defrosting mechanism comprising means to test thethickness of a layer of ice intermittently, means to apply heat to thesaid ice layer, and means response to a predetermined thickness of thesaid ice layer for closing a circuit to energize the said heat applyingmeans.

4. An automatic defrosting mechanism comprising means to test thethickness of a layer of ice, means to actuate the said testing meansintermittently, means for removing the said layer of ice, and meansresponsive to the thickness of the said ice layer for closing a circuitto energize the said ice removing means.

5. An automatic defrosting mechanism comprising means to test thethickness of a layer of ice, means to actuate the said testing meansintermittently, means for applying heat to said ice layer and meansresponsive to the thickness of the said ice layer for closing a circuitto energize the said heat applying means.

6. In refrigerating apparatus having a freezing element on which icenormally forms, an automatic defrosting mechanism comprising means t0remove ice formed on the said element a rotatable member disposedadjacent one side of the said freezing element, the said member having aportion formed as an arm extending substantially at right angles to thesaid member, a contact on the said arm, a second rotatable memberdisposed adjacent the said arm having a contact mounted thereon,resilient means between the said second member and the said arm tomaintain the said contacts normally open, and means to swing the saidsecond arm upwardly and then downwardly intermittently, the said lastmeans being adapted to close the said contacts when the ice formed is ofa predetermined thickness to energize said ice removing means.

7. In refrigerating apparatus having a freezing element on which icenormally forms, an automatic defrosting mechanism comprising a housing,a member pivotally mounted on the said housing adjacent one side of thesaid freezing element, the said member having a portion formed as an armextending substantially at right angles to the said member, a contact onthe said arm, a seco'nd member pivotally mounted on the said housingadjacent the said arm and having a contact mounted thereon, resilientmeans between the said second member and the said arm to maintain thesaid contacts normally disengaged, an electromagnet having an armatureadapted to intermittently swing past and engage the said second arm, andheating coils mounted on the said freezing element, whereby when the iceformed on the freezing element has reached a predetermined thickness,the said armature will rest on the said second member thereby closingthe said contacts and energizing the heatlngcoils to melt the ice.

8. An automatic defrosting mechanism comprising means to test thethickness of a layer of ice intermittently, means to remove the saidlayer of ice, means responsive to a predetermined thickness of the saidice layer for closing a circuit to energize the said ice removingmeans,` and means to adjust the said testing means to control thelimiting ice thickness.

9. In refrigerating apparatus having a freezing element on which icenormally forms. an automatic defrosting mechanism comprising means toremove ice formed on said element, a rotatable member disposed adjacentone side of the said freezing element, an arm on the said memberextending substantially at right angles to the said member and having acontact thereon, a second rotatable member disposed adjacent the saidarm and having a contact mounted thereon, a guard member on the arm tolimit the extent of separation of the said contacts, resilient meansbetween the said member and the said arm to maintain the contactsnormally disengaged, means to swing the said second member upwardly andthen downwardly intermittently, the said last means being adapted toclose the said contacts when the ice formed is of a predeterminedthickness, to energize said ice removing means.

10. In refrigerating apparatus having a freezing element on which icenormally forms, an automatic defrosting mechanism comprising means toremove ice formed on said element a rotatable testing device 'having onemember disposed adjacent the said freezim element, a second memberangularly disposed with respect to the said first member; contacts onthe said members, and means to rotate the said testing device to movethe said first member in the direction of the ice formed on the freezingelement, whereby when the ice has reached a predetermined limitingthickness the testing device will be brought to rest and the rotatingmeans will rest on the said second member to close the contacts forenergizing said ice removing means.

11. In an automatic defrosting mechanism for removing ice formed on acooling surface a testing device comprising a rotatable member disposedadjacent the cooling surface, the said member having a portion formed asan arm extending substantially at right angles to the said member, acontact on the said arm, a second rotatable member disposed adjacent thesaid arm and having a Contact mounted thereon, resilient means betweenthe said member and the said arm to maintain the contacts normally open,and means to move the second arm intermittently, the said last meansbeing adapted to close the said contacts when the ice formed is of apredetermined thickness.

12. In an automatic defrosting mechanism for removing ice formed on acooling surface a testing device comprising a rotatable member disposedadjacent the cooling surface, a second member angularly disposed withrespect to the said first member, contacts on the said members, andmeans to rotate the said testing device to move the said first member inthe direction of the ice formed on the cooling surface, whereby when theice has reached a predetermined limiting thickness the testing devicewill be brought to rest and the rotating means will rest on the secondmember to close the contacts.

13. In refrigerating apparatus having a freezing element on which icenormally forms, an automatic defrosting mechanism comprising means forremoving ice formed on said freezing element, a movable member disposedadjacent said freezing element and having a contact thereon, a secondmovable member operatively associated with said first movable member andhaving a contact thereon, resilient means for maintaining said contactsnormally open and means for moving said second movable member to causethe first movable member to move in the direction of the freezingelement, the said last means being adapted to close the said contactswhen the ice formed is of a predetermined thickness, for operating saidice removing means.

14. In an automatic defrosting mechanism for removing ice formed on acooling surface, a test- 'ing device comprising a movable memberdisposed adjacent the cooling surface and having a contact thereon, asecond movable member operatively associated with said first movablemember and having a contact thereon, resilient means between the saidfirst and second movable members for maintaining the contacts normallyopen. and means for moving the second movable member to cause the firstmovable member to move in the direction of the cooling surface, the saidlast means being adapted to cicse the said contacts when the ice formedis of a predetermined thickness.

GEORGE BAXTER.

